Source for parfocal shims?

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PeteM
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Source for parfocal shims?

#1 Post by PeteM » Thu Aug 11, 2022 2:08 am

I'm running low on a few thicknesses of parfocal shims - and wonder if anyone knows of a reliable source?

These tiny die-cut washers cost a penny or two to make and used to be sold in packs of 10 for around $9 mailed in a first class envelope. Fair enough. Microscope Central, usually high on everything, has them at $18 for 10 tiny washers -- seems high to me.

I'd thought Boli Optics -- which I assume sources out of India and maybe China -- might be better at $10 - but they only sent a single washer in each of the sizes ordered not the usual pack of ten. I also learned that the "real reviews" on their site are basically only 5 star with a couple 4 star thrown in. Seems my 1 star review was thrown out.

Willing to buy a bunch of these at a fair price if anyone knows a reasonable source? I try to see kids' scopes go out more or less parfocal.

Alternately, does anyone know of a source for an RMS-sized hole punch (arch-punch etc. able to cut thin brass sheet)?

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woyjwjl
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Re: Source for parfocal shims?

#2 Post by woyjwjl » Thu Aug 11, 2022 2:51 am

Try this.
1.jpg
1.jpg (80.73 KiB) Viewed 6150 times
I haven't used it. I guess so.
Micrographers from China, thanks to the forum for providing a platform for exchange

Scarodactyl
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Re: Source for parfocal shims?

#3 Post by Scarodactyl » Thu Aug 11, 2022 3:46 am

Have you tried mcmaster?

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zzffnn
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Re: Source for parfocal shims?

#4 Post by zzffnn » Thu Aug 11, 2022 4:56 am

Depending on how thick or thin the desired shim is, you may use a small rubber band. Rubber band doesn’t work too well, when the desired shim is too thin.

PeteM
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Re: Source for parfocal shims?

#5 Post by PeteM » Thu Aug 11, 2022 5:21 am

Thanks, all.

I have a couple sets of shim punches of the sort McMaster offers. The small set goes to .750 and the large set starts at .875. Both miss the .80- of RMS, but the 1" punch in the larger set has worked well for 25mm Nikon/Leica shims. These work well in brass and even thinner stainless.

Also tried a cheap 20mm gasket punch - but the hole needed to be just a bit larger. I used to have enough equipment to make up a special (heat treat oven, cylindrical grinder attachment for the lathe). Sold it ages ago (doctors told me I had 3 months to live - happily and actively living past my expiration data a decade later). You'd think someone would still be selling parfocal shims at a reasonable price?

Tiny o-rings are another solution for thicker shims - but the shims I'm out of are more like .003" to .010" thick.

Maybe I should have some laser cut out of Delrin sheet??

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Re: Source for parfocal shims?

#6 Post by Charles » Thu Aug 11, 2022 11:13 am

Try aluminum foil since they are easy to cut or punch out.

GerryR
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Re: Source for parfocal shims?

#7 Post by GerryR » Thu Aug 11, 2022 11:27 am

If you know someone with a lathe, they can bore a rod to the proper ID and turn the OD to whatever you need, then "slice" them off to whatever thickness you require. I have made several this way.

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Re: Source for parfocal shims?

#8 Post by PeteM » Thu Aug 11, 2022 3:34 pm

GerryR wrote:
Thu Aug 11, 2022 11:27 am
If you know someone with a lathe, they can bore a rod to the proper ID and turn the OD to whatever you need, then "slice" them off to whatever thickness you require. I have made several this way.
I've made a bunch of thicker parfocal shims out of aluminum tube bored to RMS inside diameter - but it hasn't worked for me trying to part off the really thin ones - .001 to .010 or so.

I might try punching out a bunch of 1" disks out of brass shim stock, stack and compress them, and then bore out the RMS diameter. Still, best if someone knows where I can buy packs of 10 or so at a reasonable cost. Surely someone somewhere is still die cutting these?

On the other hand - used to be at least three Bay Area microscope dealers who had these on hand. They've all since closed up shop. Maybe no one buying a low end scopes wants to spend to have the objectives parfocal and the top of the line scope lines are made carefully enough to be parfocal as sold?

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Re: Source for parfocal shims?

#9 Post by GerryR » Thu Aug 11, 2022 4:15 pm

PeteM wrote:
Thu Aug 11, 2022 3:34 pm
GerryR wrote:
Thu Aug 11, 2022 11:27 am
If you know someone with a lathe, they can bore a rod to the proper ID and turn the OD to whatever you need, then "slice" them off to whatever thickness you require. I have made several this way.
I've made a bunch of thicker parfocal shims out of aluminum tube bored to RMS inside diameter - but it hasn't worked for me trying to part off the really thin ones - .001 to .010 or so.
Pete, I rough drill the bore, finish the OD and then finish bore the ID. I then put a brass mandrel, to support the "tube," into the bore to do the cutoffs. The thinnest I've needed was .009 and could have gone thinner, but I doubt I could get down to .001. I screw out the objective keeping track of the angle of rotation and make the shim to that dimension, avoiding having to stack shims. I like the Parfocal distance to be such that I just need to touchup the focus a very slight amount with the fine focus knob to lower the objective toward the slide; safer for the slide with the higher power objectives. Just my way of doing it.

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Re: Source for parfocal shims?

#10 Post by zzffnn » Thu Aug 11, 2022 4:19 pm

If anyone here wants to group buy or make some popular thickness on the thinner side, I am happy to group buy. Thank you.

PeteM
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Re: Source for parfocal shims?

#11 Post by PeteM » Thu Aug 11, 2022 5:57 pm

Gerry - Good idea - your tight-fitting brass mandrel idea might help. There's been enough drag with my cut-off inserts that the really thin shims got deformed. Better lube to make sure there's not the slightest build-up of aluminum on the cut-off edge might also help.

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Re: Source for parfocal shims?

#12 Post by GerryR » Thu Aug 11, 2022 6:34 pm

PeteM wrote:
Thu Aug 11, 2022 5:57 pm
Gerry - Good idea - your tight-fitting brass mandrel idea might help. There's been enough drag with my cut-off inserts that the really thin shims got deformed. Better lube to make sure there's not the slightest build-up of aluminum on the cut-off edge might also help.
Pete, I should have mentioned that I use steel rod, 12L14 free machining steel for the shims. It cuts easily and doesn't deform when cutting off over the mandrel.

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Re: Source for parfocal shims?

#13 Post by PeteM » Thu Aug 11, 2022 6:58 pm

zzffnn wrote:
Thu Aug 11, 2022 4:19 pm
If anyone here wants to group buy or make some popular thickness on the thinner side, I am happy to group buy. Thank you.
If someone here has a decent laser cutter, I'd think Delrin / acetal shims would work be OK. Should be able to get near 144 of them out of a $30 sheet 12"x12". At, say, $10 for a pack of ten it might be worth someone's time? A single First Class stamp could mail them out.

I might try free-machining steel as Gerry does (good idea), though ideally might want something unlikely to rust.

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zzffnn
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Re: Source for parfocal shims?

#14 Post by zzffnn » Thu Aug 11, 2022 7:10 pm

PeteM, I am happy that you beat your doctor’s prediction by a decade!

Would be to join you if you take a lead . I myself don’t have the mechanical skills or machine to do it.

I don’t remember what thickness I often used: maybe the middle point of your range at 0.06”? My o rings can compress quite well; but I don’t remember what is their compression limit before they break. 0.06” is probably a safe bet.

I mostly used shim rings to parfocalize my immersion objectives. My short LOMO water apos seem to be designed shorter than their dry siblings on purpose, to prevent crushing cover slips maybe? I personally prefer them all near parfocal for speedy change, when viewing live protists.

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Re: Source for parfocal shims?

#15 Post by GerryR » Thu Aug 11, 2022 8:20 pm

PeteM wrote:
Thu Aug 11, 2022 6:58 pm

I might try free-machining steel as Gerry does (good idea), though ideally might want something unlikely to rust.
If you dip the parts in "tool black" or gun bluing, and then wipe with a light oil, they won't rust.

AntoniScott
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Re: Source for parfocal shims?

#16 Post by AntoniScott » Tue Aug 30, 2022 11:18 pm

I cut my own parfocal shims from a index card. It's was to cut the outer circle but the inner circle is difficult. The hole punch looks like it will make a cleaner inner hole.

Chas
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Re: Source for parfocal shims?

#17 Post by Chas » Tue Mar 14, 2023 11:18 am

I dont know if this is a bad idea, long term, but I printed some with PLA, the layer height on my printer is supposed to be 0.2mm, so I did a set from 0.4 to 1mm in 0.2mm steps.. the 0.4's measured as they should, the 1.0mm shims are mostly 0.05mm thinner.

They have a bit of a rough surface finish:
shims.jpg
shims.jpg (62.63 KiB) Viewed 4829 times
However they are quick to print, about 5 minutes.

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Re: Source for parfocal shims?

#18 Post by Chas » Thu Apr 13, 2023 9:07 am

This arrived in the post .....with some fuse-wire as a spacer :-)
Fuse wire.jpg
Fuse wire.jpg (108.99 KiB) Viewed 4599 times

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Re: Source for parfocal shims?

#19 Post by zzffnn » Thu Apr 13, 2023 5:20 pm

You can use tiny rubbber bands too.

PeteM
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Re: Source for parfocal shims?

#20 Post by PeteM » Thu Apr 13, 2023 5:36 pm

Or, o-rings - which come in various diameters and thicknesses suitable for around .5mm to 2mm gaps. Smaller ID ones need to be stretched (like Fan's rubber bands) to fill the smaller spaces. There is also a range over which they can be compressed and still stay put - so it's often possible to get perfect parfocality.

I've also resorted to machining a tiny bit of an objective's shoulder in cases where "less" rather than "more" space is needed.

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Re: Source for parfocal shims?

#21 Post by MichaelG. » Thu Apr 13, 2023 6:34 pm

I see that patta has made 3D Print files available here:

https://www.printables.com/model/86902- ... ms-washers

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PeteM
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Re: Source for parfocal shims?

#22 Post by PeteM » Thu Apr 13, 2023 6:55 pm

Thanks, Michael

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Re: Source for parfocal shims?

#23 Post by MichaelG. » Thu Apr 13, 2023 7:00 pm

I have just sent an eMail to a U.K. photo-etching company:

.

Dear Sirs

I am an amateur microscopist … and one of many who would find it useful to have a source of shim washers for ‘parfocalising’ sets of microscope objectives.

The basic specification is very simple:
Inside diameter 20.4mm
Outside diameter 26mm
Thickness : various, up to [say] 0.5mm
Preferably stainless steel, but not essential.

Could you please give me a first-indication of what the cost and minimum order quantities might be.

Many thanks

.
.

If I receive any helpful response, I will share it here.

MichaelG.
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PeteM
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Re: Source for parfocal shims?

#24 Post by PeteM » Thu Apr 13, 2023 10:31 pm

FWIW, I asked a similar question of a Chinese maker of stainless shims (same idea, but for auto work). Their minimum order turned out to be $200.

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Re: Source for parfocal shims?

#25 Post by PeteM » Tue May 02, 2023 8:59 pm

Following up, there is an eBay supplier of stainless steel shims for auto engine work, in thicknesses of .1 mm (.004"), .2mm, .3mm, etc. These are too wide to be used as parfocal shims but are of good material (stainless), cheap, and have either an ID or an OD dimension that's right. They can be machined to size.

The ones with a 25mm hole work for Nikon and Leica infinity objectives. I mounted them on a bolt turned down just a bit from 25.4mm (one inch) to 25mm. It was then possible to put the bolted stack in a lathe and turn the OD down.

The ones with a 24mm OD and a 17mm hole can be used for RMS standard objectives. The OD is good, the ID is too small. A two-part mandrel allows a stack of 24mm shims to be inserted in an outer tube. The stack is tightly compressed in a vise and held in place with pins - and then the 17mm ID is machined to 20.3mm.

It's a possible approach for those with access to a lathe.
.
.
25mm parfocal shims.jpg
25mm parfocal shims.jpg (116.59 KiB) Viewed 4378 times
RMS parfocal shims.jpg
RMS parfocal shims.jpg (101.4 KiB) Viewed 4378 times

MichaelG.
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Re: Source for parfocal shims?

#26 Post by MichaelG. » Tue May 02, 2023 9:48 pm

MichaelG. wrote:
Thu Apr 13, 2023 7:00 pm
If I receive any helpful response, I will share it here.
.

Presumably they are not interested :(

MichaelG.
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AntoniScott
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Re: Source for parfocal shims?

#27 Post by AntoniScott » Sun May 14, 2023 3:14 pm

Par-focal shims are available but are very pricey for what they are. I bought a hole punch and made a clean hole in an index card which fit cleanly over the objective threads. I drew a circle around the hole and cut with a pair of good scissors. The results looked very unprofessional but they did do the job.

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